Gas turbines are widely used in industrial and power generation operations. A typical gas turbine includes an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air enters the compressor, and stationary vanes and rotating blades in the compressor progressively impart kinetic energy to the working fluid (air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through nozzles in the combustors where it mixes with fuel and ignites to generate combustion gases having a high temperature, pressure, and velocity. The combustion gases flow to the turbine where they expand to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.
The combustion gases exit the turbine, and, if released immediately to the environment, would result in wasted energy generated by the gas turbine that does not produce work. Therefore, a heat recovery system is often connected downstream of the turbine to receive the exhaust combustion gases from the turbine. The combination of the gas turbine and heat recovery system is commonly referred to as a combined cycle power plant. The heat recovery system typically includes a steam generator, a steam turbine, and a condenser. The exhaust combustion gases flow to the steam generator where they heat water to generate steam. The steam then flows through the steam generator where it expands to produce work. For example, expansion of the steam in the steam turbine may rotate a shaft connected to a generator to produce electricity. The shaft and generator may be the same shaft and generator connected to the gas turbine, or the gas turbine and heat recovery system may operate using separate shafts and generators. The condenser downstream of the steam generator condenses the steam to condensate, and condensate pumps direct the condensate back to the steam generator. The heat recovery system thus captures energy from the exhaust combustion gases before they are eventually released to the environment, thus increasing the overall efficiency of the combined cycle power plant.
The steam generator is typically located in or upstream of a vertical stack that allows the exhaust combustion gases to naturally rise across tubes in the steam generator to enhance steam generation. In some instances, a customer may limit the height of the vertical stack, resulting in a corresponding limit in the size of the steam generator and the amount of steam that it may produce. In addition, the gas turbine often includes one or more heat exchangers associated with auxiliary components, and the heat removed by these heat exchangers is often not recaptured, thus reducing the overall efficiency of the combined cycle power plant. Consequently, there is a need for systems that makes more efficient use of the heat extracted by the heat exchangers of auxiliary components while increasing steam generation, particularly in systems having vertical stacks of limited height.